For example, in the drive system of spindle motors of HDD devices, reduction in rotational pulsation is strongly desired. If the rotational pulsation is large, read or write error occurs, which becomes a great impediment in enhancing the recording density. Furthermore, the rotational pulsation is preferably as small as possible to reduce the noise that HDD devices generate.
Accordingly, in recent years, a technology to make a waveform of driving current of the motor to an ideal sinusoidal current has been the mainstream (e.g., Japanese Patent Application Laid-Open Publication No. 2005-102447 (Patent Document 1)). In principle, the rotational pulsation can be suppressed by driving the motor by sinusoidal current.
Further, as Driving methods which suppress the rotational pulsation itself, a method of tabling a pulsation pattern in advance and correcting the same (e.g., Japanese Patent Application Laid-Open Publication No. 11-103588 (Patent Document 2)), a method of estimation calculating a disturbance torque component, which is a factor of pulsation, with an observer and performing a control to cancel such disturbance torque component (e.g., Japanese Patent Application Laid-Open Publication No. 2001-352789 (Patent Document 3)), and the like have been proposed.